The applicant hypothesis is that immunity to Entamoeba histolytica infection is acquired from previous infection. In specific aim 1 a 3 years prospective study will measure E. histolytica infection and invasion in cohorts of children ages 2-5 in the Mirpur district of Dhaka. If the hypothesis is correct they would predict that following outcomes: a) Children who had prior E. histolytica infection will be less likely to have future of invasive amebiasis; b) it is possible that they will also be less likely to be reinfected with E. histolytica; and, c) if reinfected may clear infection more rapidly. If their hypothesis is correct they would predict that clearance of E. histolytica infection will be associated with the development of an adherence-inhibitory antibody response against the carbohydrate-binding domain of the lectin. Completion of these studies should provide a foundation for understanding the mechanisms of protective immunity to amebiasis, and provide a baseline for evaluating the efficacy of vaccines as they enter clinical trails.